body {
  margin: 0;
}

.footer {
  position: relative;
  height: 50vh;
  margin-top: 50vh;
  background: pink;
}

.bubbles {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 1em;
  background: lightblue;
  filter: url(#blob);
}

.bubble {
  --x: 100px;
  --s: 50px;
  --d: 2s;
  position: absolute;
  border-radius: 50%;
  background: inherit;
  width: var(--s);
  height: var(--s);
  left: var(--x);
  top: 30px;
  animation: bubbling var(--d) ease-in forwards;
}

@keyframes bubbling {
  75% {
    transform: scale(1);
  }
  to {
    transform: scale(0);
    top: -200px;
  }
}
